Investigate possible issue on handling the response for delta submission

[cristianciutea]

In the delta store.go, we handle the response from the platform on delta submission.
There are different scenarios when the platform can reject the deltas, providing a hint on fixing the issue.
The is a case when platform expected a delta ID that is higher with 1 than the one sent.
During an investigation, I've noticed that the delta cache file is not updated in this case. (the file is updated by calling SaveState method).
We should check why this is happening and if it's expected (the comment in the code states that is the "normal case", so maybe is the expected behavior). Also we should sync with the platform to see if we should save the "id" or the "SendNextID"

current code:

case resultHint.SendNextID == id+1:
			// Normal case.
			p.setLastSentID(entityKey, id)

Steps to reproduce:

• clean /var/db/newrelic-infra/data directory
• (optional) clean logs
• Change the display_name to a new one, so a new entityID is created in the platform
• Start the agent and tail the logs. You can grep by 'hint.'
• Check the delta /var/db/newrelic-infra/data/.delta_repo/delta_id_cache.json file and see if last_sent_id has been updated